The disclosure relates to an electromagnetic rail braking device having a magnetic base body and/or support body, a pole shoe section, the pole shoe section comprising a magnetic-flux-guiding area as well as a magnetic-flux-cutting area.
In principle, electromagnetic rail brakes involve an electromagnet consisting of a coil extending in the rail direction and horseshoe-like magnetic cores. The direct current flowing in the magnetic coil causes a magnetomotive force which generates a magnetic flux in the magnetic core, which magnetic flux path is closed by the rail head. The amount of the braking force of an electromagnetic rail brake depends on the magnetic reluctance of the magnetic circuit. That is, the geometry and permeability, the electric flux, the coefficient of friction between the magnetic shoe and the rail as well as the rail condition.
In principle, a differentiation can be made between two different types of magnets based on the construction of the brake magnets. In a first embodiment, the magnetic core consists of two steel cheeks which are firmly screwed to the coil body on both sides. As an alternative, the brake magnet can also be constructed as a link magnet. In the case of such an embodiment, the magnetic core is divided into two end pieces and several connecting links. The end pieces are firmly screwed to the coil body, and the links can move freely in the coil box opening and follow the unevenness of the rail.
Concerning the construction of electromagnetic rail brakes, reference is made to the publication “Brakes for Rail Vehicles”, Manual of Brake-Related Terms and Values, Page 45, by Knorr-Bremse AG, München, 1990.
In the case of electromagnetic rail brakes according to the state of the art, St37 steel is preferably used for friction materials in the pole shoe section. The use of a St37 friction layer has the disadvantage that buildups occur increasingly which considerably reduce the braking force of the brake. In order to restore this braking force, it was necessary to manually remove the buildup, which caused high maintenance costs. Although the use of GGG40 cast steel resulted in less buildup, only low braking forces could be applied by such friction layers.
A friction material which is distinguished by a low buildup tendency and permits a sufficient service life is, for example, a sintered material as a friction material for the pole shoe section. The sintered material contains at least one fraction of pulverized wear inhibitor and one fraction of a protective-layer-forming powder.
A disadvantage of the use of sintered materials as the friction material was the problem that, as the wear of the pole shoes increased, the holding force and therefore also the braking forces to be generated increased considerably. These braking forces rose to twice to three times the forces in the worn condition.